The present invention relates to an apparatus for hulling pistachio nuts and separating the hulled pistachios from the hulls.
Pistachio nuts have a hard shell around the edible kernel and a pericarp or hull which encases the shell. The hulling of pistachios is difficult and present some unusual problems. The hulls of pistachios are stronger, more tenaciously adherent to the shells, and more difficult to remove than the hulls of many nuts, particularly if the pistachio is not yet ripe. If the hull is not promptly removed from pistachios after harvest, it discolors the shells requiring that the normally attractive straw colored shells be colored to hide undesirable stains. For this reason, most commercial pistachios are dyed an unnatural and undesirable pink or red color to obscure the stains. Even when abundant hand labor is available, it is usually not feasible to hull sufficiently large volumes of pistachios soon enough after harvest to avoid shell discoloration. As a result, mechanical hullers of various configurations have been developed.
Mechanical hullers such as that disclosed in U.S. Pat. No. 4,034,665 use a great deal of water in the hulling process. As fresh water becomes a more expensive and scarce resource, using a large amount of water in the hulling process becomes less advantageous financially and environmentally.
Therefore, there is a need in the art for a pistachio hulling machine which may operate with minimum water usage or without water usage.
In general term, the invention provides a method and apparatus for hulling pistachio nuts and separating the hulls from the pistachio nuts. The pistachios to be processed are deposited in between counter-rotating rollers having a resilient, frictional and preferably textured outer surface. A main roller has a larger diameter than a satellite roller, however both rollers are rotated at the same rate. As a result, the outer surfaces of the main and satellite rollers travel at different speeds. The outer surface of both rollers may comprise a high-friction material such as a rubber. As a result, the friction created between the pistachio hull and the rollers ruptures the hull and peels it away from the pistachio shell. On many pistachios, the ruptured hull remains attached to the shell by a tag end. The pistachios and attached and unattached hulls then are dropped onto an elongate roller. The elongate roller separates the hulls from the pistachio shells and other debris. The hulls and debris drop underneath the elongate roller. The pistachio shells are augured to one end of the elongate roller by the elongate roller and collected for further processing.